SAN FRANCISCO (KTVB/AP) -- A federal court hearing is underway over gay marriage bans in Idaho, Nevada and Hawaii, with a lawyer defending the state of Idaho's ban facing tough questions from a judge on the panel.

Attorney Monte Neil Stewart told the three-judge panel of the 9th U.S. Circuit of Appeals in San Francisco on Monday that same-sex marriage would undermine children's right to be raised by a male father and female mother.

Judge Marsha Berzon questioned how gay marriage differed from the current model of marriage, which she called "genderless."

An attorney representing gay marriage supporters opposed to Idaho's ban is scheduled to speak next, with the court expected to hear arguments over Nevada and Hawaii's bans after that.

The 9th Circuit in 2012 invalidated California's gay marriage ban because it singled out a minority group for disparate treatment for no compelling reason. The U.S. Supreme Court dismissed the case last year without ruling on the legal merits of gay marriage.

The arguments are the latest at the federal court level where same-sex wedding proponents have gained numerous victories.